Geochemical prospecting



March 28, 1944. R, T y SANDERSQN 2,345,219

GEOCHEMICAL PROSPECTING Filed Dec. 30. 1959,

uses of my invention will become Patented 'Mn- 2 8.` 1944 U-NITEV v'sfnrrlss PArEN'r :oFFlcE asoma Gnocnnmcap rao'srnc'riNG v neben nomia senaemn. siem me, om.. assigner' to Stanolind Gal company,

kla.,a corporatlonofnelawarc- .innemen is, ma serai Ne. mais 11cmm. V am f 'rms mennen relates 'to een" analysis .and to soil -gas analysis and more particularly to soil analysis and soil gaseanalysisfor purposes of geochemical prospecting.- Still more particularly and the like for analysis'as a'. step in the art of 'geochemical prospectingll In recent 'years increasing attention has been given to the analysis of soils as' an aid to they lo- -it relates to the collectionoi samples of soil gas .stituents'of the pear. it 'is of great importance to' protect the hydrocarbon sor t from various sorbable congases other than those which it is desired to measure. Thus'it'is often desirable to exclude carbon dioxide and ammonia and when using a solid adsorbent it isimperative to exclude A water br maintain constant humidity'.

lcation-oi' deep seated oilq and gas deposits. Thel0 theory commonly nem iethat hydrocarbon materials migrate upward from deep seated `deposits and are sorbed by the soils. 'Ihus by analysis of j these solls for hydrocarbon materials and in some' instances for related materials such as hydrogen, l5

some indication of they presence of deep seated petroleumdepomts canbe had. M

However, diiillculties" 'are encountered in vthis method of geochemical prospecting due to the fact a survey it is difilcultto determine whether anomalies are due entirely lto sub-.surface conditions or whether they are due in 'whole or in part todiiferences in sorptive capacity or retentivity.

Furthermore, not only do soils vary markedly in sorptivelcapacity due tfvaratio/ns inthe chemical and physical compositions but the concentration oi hydrocarbons and other materials ina given soilmay also be dependent on the environmental 3.0 history of the soil which cannot be known with.

certainty and which may Adifl'er from survey station to survey station.

It is a purpose of my invention to overcome) these diiliculties'and to provide'a method of and 3 5 apparatus for geochemical prospecting which will r give-more significant andN comparable results than the methods and apparatus heretofore used: It is also an object of my invention to .provide a. particularly convenient Imethod of sample collection 40 in connection with geochemical prospecting. Af' further object of my invention is to standardize the collection of samples of volatile soil gas components, particularlysoil gas hydrocarbons. A. still' further object oi" my 'invention is to provide 45 samples of soil gas hydrocarbons relatively free from contaminating constituents. Still another object is to provide samples of high concentration. Other and more Kdetailed objects, advantages and description thereof proceeds. I accomplish these objects by placing in proximity tothe soil in-question a body ofa standardized sorbent having a nuch higher sorptive power than'the soil itself. will hereinafter aps that the sorptive capacities and retentivities of 20, Asurfil.ce' soils vary widely'so .that in the course of Various materials can be used as sorbents for .801,1 hydrocarbons in practicingmy invention. but the .materialchosen shoul readily reclairnable or charcoal, 'activated carbon and lmuarearbonaceous sm'bents eomonly -known as activated charcoal are preferred but any other material having a' high and/or specific sorptive capacity for hydrocarbon, hydrogen. etc., can-be used. Comactivated' charcoal is not generally satisftory as such' since it is usually contaminated with non-constant amounts of hydrocarbons or e' gases which interfere with the hydrocarbon sorption'and especia11y, wlth the subsequent analysis.

commercial anvated`charcoarmust thereforebe thoroughly de by some such-method as prolonged heating at a high temperature in vacuo before it is ilt for use as a standard sorbent in 'accordance with my invention. By the way of apparent as the 00 i containers for thsrsorbent or sorbents.

iecting the charcoal to those to be tested results in theI displacement.,

of strongly sorbed 4impurities which' may not otherwis'evbe eliminated. After such pretreatment followed by degassingtheS specific sorptive capacity of the activated charcoal for hydrocarbon gases is higher than if the pretreatment is..

omitted. e The degassed contact with the soil or a layer of a desiccant can be plaeednextetothe soiland'thesorbentcan be placed in. contact, with the desiccant. However, it is very strongly preferred to use a container or Thus the preferred method of practicing my vention is to place' a weighed amount o f standsorbent into properly designed open conbe inexpensive or .It shouldalo'be.- available asa veryuniiorm, well standardized sorbent een be placed in 1n-eci:

.made with post hole augersorotherwise.

tainer `and lower the container to desired vdepth into a hole in the surface soil. seal the hole from the atmosphere, leave the container in place for a measured period of time, remove it fromthe hole, transfer the sorbent to a closed container (or close the original container) and then transport the sorbent to a laboratory where the hydrocarbons in particular and also other 'substances of interest such as hydrogen can be removed by methods normally including the-use of heat and vacuum and can be analyzed by various known means.

.In the` course of a geochemical prospecting operation thisl method is, of course, carried out foreach of a considerable number of survey stations located at suitably spaced points, for instance every tenth mile along a survey line or similarly spacedover a survey area. The results are `plotted Aor compared and high values indicate the presence of underlying, or underlying and ad jacent, deep-seated petroleum deposits.

It is preferred that the sorbent be in contact with or in juxtaposition/to the soil at a depth of at leastv three feet rather than having it in juxtaposition to the soil precisely at the surface since there isa tendency for contamination at the sur- -Various depths can beV used, preferably 3 face. to 25 feet, for' instance 6 or 8 feet.

Certain methods of applying myinvention are illustrated by way ofexample in the accompanying drawing in which:

v Figure 1 is a section through a portion of the surface soil showing one method of applying my surface may have' nomore ready access to 'the sorbent than the soil atmosphere; preferably far less ready access than the soil atmosphere.

- This sealing of thev hole from the upper atmosphere can be accomplished in a preferred manner, as shown in Figure 2, by excavating an enlarged hole Il at thejupper part of hole II and placing cover I4 at the bottom of this enlarged hole. After cover vI4 carrying sample container I2 has been put in place the enlarged hole l I! can be filled in with earth I6 or otherwise to do a thorough sealing job. Rope I1 attached to 'cover I4 is allowed to protrude above the surface to serve as a marker.

I'he sorbent should be left in position for a period of at least several hours, for instance overnight andit is sometimes desirable to leave it inl place for a matter of several days or even several weeks. For any given survey, of course, the

sorbent used at the various survey stations should be identical in 'nature and condition,` equal in amount; should be similarly spaced with regard to the soil and should be left in place for the same length of time. time the sorbent is in place be constant from survey station to survey station Ibut the actual period should be the same insofar as is conveniently possible since temperature conditions and other factors are not without effect. Thus one sample left inplace for 24 hours on a hot day might not be comparable with results obtained at another survey station on a cooler day.

Afterthe sample has been left in communication with the soil as shown in Figure 1 or Figure 2 for thedesired period, it or a selected part ofit is removed, for instance, by careful manipulation or by the use of known sampling devices, and takento the laboratory forl analysis as previously sorbent can; of course, be placed in the bottom of such a hole without using the container but the container is preferred. Moreover, in order to avoid Athe possibility that the sorbent will be wet by water accumulating incthe bottomfof the hole it is preferable rthat the container be' supported above the bottom of the hole. Thus, for instance, the hole II can be 8 feet deep and the container I2 which may, for instance contain 100 grams of activated charcoal can be supported at a depth of 5 feet. This container I2 is open at both ends and is supported by a chain or cord I3 ,fronna cover i4 which serves various purposes including that of preventing contamination and ingressA of surface water vinto the hole. Another important purpose served by cover Il is that ofl preventing the upper atmosphere above thesoil from diffusing over the sorbent more readily than the soil atmosphere. If the upper atmosphere .could diiuse over the sorbent readily, even if there were no resultant contamination,the

'effective Yaverage concentration of hydrocarbonsl in the atmosphere about the sorbent would be less than that of the soil atmosphere, and consequently the rate of sorption, or amount of sor tion in a fixed period of time, would be lower, and the proportional decrease would vary from location to location. It is therefore important to close the hole so that the atmosphere above the described.V

As .shown in rFigures 3, 4 and 5, one suitable -form of container is provided with a screen II on whichflthe sorbent or sorbents rest and the sides of the container extend both above and below that part ofrthe container which is illled with I sorbent or sorbents. The upper and lower parts of the side wall of the container are provided with openings I9 which cooperate with openings 2l in caps 2|, Also in a preferred form, the top and bottom oi' container I2 are provided with removable inner covers 22 having openings 23 which cooperate with openings 24 in caps 2|; As seen in Figures 3 and 4, the container is open both at the upper and lower parts of the side wall and at the top and bottomto provide maxi mum ventilation or, lin other words, vmaximum ingress of soil gas to the sample container. In

Figure 5the openings and 24 are shown in yclosed position and with' caps 2| in this position the side wall openings are likewise closed. The container is, of course, kept in closed condition except when actually in place in Iiuxtaposition to the soil.

One complicating factor in the method which I have devised is the effect of water sorption on the sorption of hydrocarbons. Thus, if the amount of water present varies markedly, the amount of hydrocarbon sorbed'may be influenced bythe water sorption. This can'be minimized by the use of sorbents which have a selective or specific effect on hydrocarbons-as compared with water. 'I'his is true of activated charcoal and `the like to a limited extent and is markedly true of heavy hydrocarbon oils, petroleum Jellies, etc.,

the use of which will be mentioned'hereinafter. In using solid adsorbents it is important, in

Not only should the length of Y i'or instance magnesium perchlorate, can be` used.

asumo f fact practically` imperative, to provide some solution for the problem ot errors introduced by "water sorption. This can be done by various .methods which the simplest isfmerely to'use the sorben in an initially thoroughly dry condi- I tion. 'Ihis,'however, is nota complete solution of the'A problem fsince 'non-uniform sorption of waterLvapor during the sampling operation causes non-uniform effects on ,the hydrocarbon sorptionv.

l Perhaps the best solution isl to control the l0 'humidity ot the atmosphere to which the sorbent is subjected. Thus, for instance,fan excess of water can be `placed in the bottom of the hole in a separate container sothat the atmosphere 1 .in the hole is always 'saturated with water. This l5 .,-g'rive'suniformity but greatlyreduces' the sorptlve wer of the/'sorbent for hydrocarbons. vMorethe porosity .of thesoil and the constant J 0f' gaseshlntothe hole makes this method relatively e. e A;-Apcordingly itis much better to achieve unliormity by keeping thehumidity low rather than i. e., by keeping the atmosphee in the hole as dry as possible. One way of accomplishing I this is by putting luto the bottom of the hole a '25- quantity of dehydrating agent, for instance calcium'chloride' although this is by no means an ideal solution ,to the problem because of the con- 'stantingresg ofmoisture-ladeny gases into the` vhole from the soil. lA ia'r better.method is that v-30 shown in Figure il -in which the dehydrating agent is in immediate proximity to thel sorbent.

As illustrating the problem, an activated charcoal which adsorbed 1.15% of its weight'of water when exposed to air containing water vapor hav- 35 a' partia'lpre'ssure of 5 .15 millimeters of merbsorbed 39.33% of water -when the partial was 23.76 millimeters of mercury.l These dierences in.water sorption greatly aii'ect the hydrocarbon sorption and thus lead tonon-com- 40 parable results. On'the other hand, thissame' activated'v charcoal; would sorb vonly 0.15% of water from air dried over anhydrous or relatively anhydrous 1 'chloride .and when A-all samples in a given ,survey are taken in atmospheres 45 thug dried the effect voi' waterbecomes completely fB81i81ble. 1.

Instead of 4calcium chloride other desiccants,

Icjis sisodesirbie to protect the sorbent for 5 'I bons fromacidiciand basic gases,.such as carbomdioiide and ammonia. yAscarite (e.v eommeinmariai containing ptessium nydroxide a d asbestos) or fused lpotassium or hydroxide or other basic or sikeiine re- 55 'agents used as acidic gas removal reagents while bisulfate and variousacidic reagents be uiiediasfragents for removing ammonia f l 't'jalkaline or basicga'ses. l u shows a large mass 25 of standardized 60 sorbent, e. g., dried, degassed .actif f carbomf'above ,and below it'thlck layers, 2.8 of water sorbent. e. g., calcium chloride, then thin layers 2l of carbon dioxide removal reagent, e. g.; Ascaritmnent thin layers 2l of 'ammonia removal 05 agent, e. g., ,sodium bisulfate, and on the outside if deaireithlck layers 2Q of a .water removal agente:"g'., calcium. chloride. One or more of layers 2Q, 21, 2l and 2l can be omit The" sequence' of the'layers canbe varied so long as 70 thejhydrocarbon sorbent ison the inside. However-iff is generated by one of the other ...orienta for instance by the interaction of-KOH a'layeror layers of water removal agent sbouldisurround -the hydrocarbon sorbent.

from them either physically or chemically, so as For the lmost part my invention has been rclescribed in connection withthe use'of solid adsorbents for taking the hydrocarbon samples.

. Howeve'r, other sorbents, for instance liquids such as 'heavy mineral oils and semidluld materials such as petroleum jellies can also be used. These materials do not have the surface sorp'tion'action typical of activated 'charcoal andthe likev but do have a good sorptive-action or solvent power for hydrocarbons, such as the'light hydrocarbons foundin soll gases. Moreover, thesev hydrocarbon solvents have the greatadvantage that they are e not likely to be seriously affected by water, carbon dioxide, ammonia, etc., -so that.it is not mercial composition containing lubricating oil and petrolatum wax) was found to be a sorbent forgaseous hydrocarbons. Moreover, these can .e be driven off foranalysis by heatlngJat 210 C.

for fifteen minutes under a moderate vacuum@ -Y When using a solid adsorbent such'as activated charcoal the sorbed hydrocarbonscan be driven oil' by heating -the sorbent inivacuo or in astream of inert gas. For instance they can be driven oil by heating for 30 minutes-at a temperature of 250 C. under a pressure of 10-'5 millimeters of mercury. The hydrocarbons thus driven oi! can be puried, condensed in a liquid air orv liquid nitrogen trap and analyzed or measured by various methods known to the art.

The methodsV outlined in the preceding paragraph lor driving off the-sorbed gases are often not entirely satisfactory since the gases are not completely driven ofi at convenient temperatures in a reasonable time while at higher Atemperatures decomposition of the sorbed gases and chemical reactions between some ofthe various substances present are likely.VV

I propose, therefore, that Athle sorbent contain- -ing the gases to be analyzed be treated with an The and to simplify their' subsequentl separation. sorbed gases t'o be analyzed are displaced separatedv for final analysis.

This displacement method is also applicable samples ofthe soil ltself. v 'I'he displacement substance should ideally be: (l) JStrongly sorbedby the sorbent or soil, and therefore; preferablypof' low rnolecular volume; and

A(2) Easily separable from the hydrocarbbns to be measured; hence, y .A

(a) Of diierent volatility than the hydrocar- /bons`, preferably 'less volatile;

(b) Stable toward moderate heat;`

(c) LChemically inert with respect to hydrocarbons; j v

(d) Relatively active chemically.

As examples of such displacement substances ammonia or organic. amines can be used and \to the soil or sorbent in amounts ranging from 1% to 100% of thel soil or sorbent. Some heating is ,then usually necessary but no more (often much used. and the separation of hydrocarbons from the` sorbent is more nearly' complete. Vacuum and/or y-a stream of inert 'gases can be used to 'help re-- n The displacement substance'. is vthen removed fromthe move the originally sorbed substances.

displaced' gases 'byphysical or chemical means I' less) thanl Awhen no displacement substance is sorbent, removing said containers from the holes after substantially equal periods of time sufcient Y to permit enough hydrocarbons `to be sorbed by the sorbent, removing at least part of said bodies of sorbent from the containers, displacingsorbed hydrocarbons from said sorbent by addinga displacement substance thereto, and'analyzing the and thedisplacedrgases are measured or analyzed.

While I havedescribed my invention in cony vnection with certain vpreferred embodiments thereof, it will be understood that-these are by way of illustration rather than by way of limita` tion and that I' do not mean to be restricted thereto except as deflnedin the appended claims.

I claim: f l. Amethod of geochemical'prospecting 'com- `prising placing `a container containing `astandard body oi' sorbent 'for hydrocarbon vgases in holes vlocated in accordance with a spaced survey pattern, said sorbent beingprotected by at least one j material which will'remove at least one soil gas constituent selected from the group vconsisting n free access of the yhydrocarbon constituents to' hydrocarbonsvthus displaced.

5. A method of geochemical prospecting comprising placing a container containing a. standard body of sorbent for hydrocarbon gases in holes located in accordance with a spaced survey pattern, said soIrbent being protected by a material which.. will remove carbon dioxide from the atmospheres in the holes but which will permit said sorbent, removing said containers from the holes `after substantially equal periods of time suilcient toI permitV enough hydrocarbons to be oi' water vap'or,ac'idic constituents and alkaline constituents from the atmospheres in the holes but which will permit free access of the hydrocarbon constituents to said sorbent, removing said containers from the' holes after substantially equal periods of time. suiilcient to permit enough hydrocarbons to be sorbed by the sorbent, re,`

moving 'at least part ot-said bodies or sorbent ,fromihe containers, displacing sorbed hydrocarbons from said sorbent by adding a displacement substance thereto, and analyzing the h y= drocarbonsthus displaced. s

2. A-method of geochemical pr specting comprising placinga container containing a standard body of sorbent for hydrocarbon gases in holes located in accordance with a spaced survey pattern, said sorbent being protected by a material which lwill remove acidic constituents from the atmospheres in the holes but. which will permit `free access of the hydrocarbon constituents to said sorbent,y removing saidggcontainers from the holes after substantially equal -periods of time suilicient to permit enough hydrocarbons to be sorbed by the sorbent, removing at -least partl of said bodies of sorbent from the containers, displacing sorbed hydrocarbons from said sorbent by adding adisplacement substance thereto, and

` analyzing the hydrocarbons thus displaced.

3. A method of geochemical prospecting comprising placing a container containing a standard sorbed by the sorbent, removing at least part of said bodies of sorbent from the containers, dis- -placing sorbed `\hydrocarbons from Isaid sorbent by adding a displacement substance thereto,v andV analyzing the hydrocarbons .thus displaced. i

6. A method of geochemical prospecting comprising'placinga container containing a standard body of sorbent for hydrocarbon gases in holes located in accordance witha spaced survey pat# tern, said sorbent being protected by a material 1 prising a container, a massl `of hydrocarbon -sorbent in saidcontainer.' said container being provided with openings to subject said sorbent to soil gases, a layer of a chemical reagent disposed between said openings` and said sorbent,

- said chemical reagent having a selective removal body of sorbent for hydrocarbon gases in holes located in accordance with a spaced survey pattern, said sorbent being protected by a material whichwill remove alkaline constituents from the atmospheres in the holes but which will permit.

free access of the hydrocarbon constituents to 4 said sorbent, removing said containers from the holes after substantially equal periods of time `suillcientto permit enough hydrocarbons to be sorbed by the sorbent, removing at least part of. said bodies of sorbent from the containers, displacing sorbed hydrocarbons from said sorbent by adding a displacement substance thereto, and

- analyzing the hydrocarbons thus displaced.A

4. A method of geochemical prospecting comprising placing a container containing a standard located in accordance with a spaced 'survey pattern, said sorbent being protected by a material which will remove water vapor, acidic constituents and alkaline constituents from the atmos.

pheres in the vholes but which will permit free access .of the hydrocarbon constituents to said action on at least one soil gas constituent selected from the group consisting of water, carbon dioxide and ammonia,vand means connected to said container for suspending4 said` container in a shallow Well and for minimizing access of atmospheric air to said container.

8. Apparatus 'for geochemical prospecting comprising a container, a mass of hydrocarbon sorbent in said container, said'container being vbpdy of sorbent for hydrocarbon gases in holes v provided with openings to subject said sorbent to soil igases, a layer'of a water removal reagent disposed between said openings and said sorbent, a

separate layer of a reagent for the removal of y gases selected from the group consisting of acidic and basic gases disposed between said iirst-mentioned layer and said sorbent, and means for suspending said' container in a shallow well.

9. Apparatus for geochemical prospecting comprising ,a container, a mass. of hydrocarbon sorbent in'said container, said container being provided with openings to subject said sorbent to soil gases, a layer of a water removal reagent disposed between said openings and said sorbent,

a separate layer of a reagent for the removal of gases selected from Ithe group consisting of acidic and basic gases disposed between said first-mentioned layer and said` sorbent, a second layer of a water removal reagent disposed between said last-mentioned layer and said sorbent, and -ior suspending said container in a shallow weil.

10. Apparatus for geochemical prospecting comprising a container, a mass oi hydrocarbon 'sorbent in said container, said container being provided with openings to subject said sorbent to comprising a container, a sorbent in said container, fsaid container being provided with openings to subject said sorbentto soil gases, a layer of a water removal reagent disposed between said openings and said sorbent, separate layers ofy reagents for the removal of acidic and basic gases disposed between said firstmentioned layer and said sorbent, a second layer of a Water removal reagent disposed between said last-mentioned layers and said sorbent, and

means ior suspending said container in a shallow well. l THOMAS SANDERSON mass of hydrocarbon 

